Dosing pump

ABSTRACT

The invention provides a metering pump having pistons ( 13, 13 ′) which lie opposite one another, are guided in cylinders ( 11, 11′ ) and are connected to one another by a slide ( 14 ) which is moved in a reciprocating manner by a drive motor ( 201 ), a switching device ( 3 ) being arranged between the pistons ( 13, 13 ′) in a valve block ( 2 ), which switching device alternately connects the opposite cylinder spaces to a suction opening ( 4 ) and a delivery opening ( 5 ).

[0001] The invention relates to a metering pump, in particular a metering pump for small delivery quantities.

[0002] The invention is intended to propose a metering pump which has a simple structure and can be used for a wide range of metering purposes, in particular with small delivery quantities.

[0003] According to the invention, this is achieved by a metering pump as described in claim 1, in which a simple metering pump structure results from a switching device being arranged between pistons which lie opposite one another and are connected to one another by a slide.

[0004] An exemplary embodiment of the invention is explained in more detail below with reference to the drawing, in which:

[0005]FIG. 1 shows a front view of the pump unit in section on line I-I in FIG. 3,

[0006]FIG. 2 shows a sectional illustration of a piston,

[0007]FIG. 3 shows a section on line II-II in FIG. 1,

[0008]FIG. 4 shows a back view of the pump unit,

[0009]FIG. 4a shows a view of the snap-action device,

[0010]FIG. 5 shows a perspective view of the metering pump with the drive unit separated from the pump unit,

[0011]FIG. 6 diagrammatically depicts the drive train between motor and slide, and

[0012]FIG. 7 diagrammatically depicts a sectional view of a further embodiment.

[0013] A valve block 2, which in a conical bore (FIG. 3) receives a correspondingly conical control cock 3, is secured to a base plate 1 of a pump unit 100 (FIG. 5) by means of screws 21. As shown in FIG. 1, the valve block 2 is provided on the underside with a suction bore 4, and, diametrically opposite, on the top side, with a delivery bore 5, grooves 6 and 7 being formed on the circumference of the control cock 3 in the region of these bores 4 and 5, these grooves in each case extending over approximately half the circumference and being separated from one another by webs 8 and 8′. Furthermore, cylinder bores 9 and 10 are formed opposite one another on the sides of the valve block 2 in the region of the grooves 6, 7, and cylinder tubes 11 and 11′ are fitted to the cylinder bores at the end sides and are held clamped between a holding plate 12 and 12′ and the valve block 2 by the holding plate.

[0014] In each case one piston 13 or 13′, the piston rod 30 of which is secured to a slide arm 14′ or 14″, respectively, is in each case guided in the cylinder tubes 11 and 11′. A slide 14 which connects the two slide arms 14′ and 14″ to one another is guided in a guide 15 on the rear side of the base plate 1 (FIG. 4). This slide 14, which is approximately U-shaped when seen in plan view as in FIG. 3 and has the perpendicularly protruding slide arms 14′ and 14″, is moved in a reciprocating manner by an electric drive motor which is accommodated in a drive unit 200 (FIG. 5). As is diagrammatically indicated in FIG. 6, the electric motor 201, via an intermediate gear 202 which comprises for example two meshing gearwheels, drives a threaded spindle 203 with which a nut 204, which is connected to the slide 14 via a protruding bolt 205, is in engagement. The direction of rotation of the motor 201 is switched over by limit switches 206 and 207 when an actuating element 208 arranged adjustably at the nut 204 comes to bear against the corresponding limit switch 206 or 207 when the limit positions of the pistons 13 and 13′ are reached.

[0015] In the exemplary embodiment illustrated in FIG. 4, shoulders 16, which are displaceable in a recess la in the base plate 1 and at each of which a stop pin 17 or 17′ is arranged in such a manner that it can be adjusted by a screw thread, are formed at a distance from one another on the slide 14. These stop pins 17 and 17′ interact with a lever 18 which is arranged eccentrically on the rear side of the control cock 3 in such a manner that on contact with one of the stop pins 17, the control cock 3 is pivoted through a predetermined angular range about its axis, in order that the control cock 3 be pivoted during the changeover from the delivery stroke to the suction stroke of the pistons.

[0016] In the operating position shown in FIG. 1, the piston 13 is located at the end of the discharging movement, during which the medium contained in the cylinder tube 11 and in the circumferential groove 6 of the control cock 3 was discharged through the delivery bore 5 located at the top, while at the same time the piston 13′ has executed a suction movement, as a result of which medium has been sucked into the circumferential groove 7 and into the cylinder tube 11′ through the suction bore 4 lying at the bottom.

[0017] By reversing the drive motor 201 by means of one of the limit switches 206 and 207, the slide arms 14′ and 14″ are moved to the left out of the position shown in FIG. 1, while at the same time the control cock 3 is pivoted by the lever 18 in the counterclockwise direction in FIG. 1, by the stop pins 17 on the slide 14 in such a manner that the webs 8 and 8′ come to lie in each case on the other side of the suction bore 4 and the delivery bore 5, so that the delivery stroke of the piston 13′ conveys the medium which has been sucked in via the circumferential groove 7 to the delivery bore 5, while the piston 13 sucks in medium via the suction bore 4 and the circumferential groove 6.

[0018] The lever 18 may be arranged on the control cock 3, so that the control cock 3 is switched over directly by the stop pins 17. To accelerate the switching movement of the control cock 3 by the slide 14, it is preferable to provide a spring-loaded snap-action device. In the embodiment shown in FIG. 4, the lever 18 is formed so as to protrude radially at a peg 42 which is mounted rotatably in a bore 214 in a housing 220 in the drive unit 200 via a ball bearing (FIG. 3). The lever 18 on the peg 42 is configured as an eccentric which engages in an approximately V-shaped recess 44 on the rear side of the control cock 3. FIG. 4 indicates the recess 44 which widens radially outward. Furthermore, as shown in FIG. 4a, a radially protruding lever 19 is inserted at the peg 42 via a polygonal peg 43, on which lever a spring 20, the other end of which is secured to the housing 220, engages (FIG. 3). As soon as, for example, the stop pin 17′ comes to bear against the eccentric lever 18 and has pressed the latter a certain distance to the right in FIG. 4, the tension spring 20 is moved beyond a dead center position, with the result that the spring pivots the peg 42 and therefore the eccentric lever 18 with a snap action, so that the control cock 3 is switched over into the intended pivoted position at an accelerated rate. The same procedure takes place at the opposite stop pin 17, with the spring 20 coming to lie on the other side of the dead center position as a result of the stop pin 17 bearing against the eccentric lever 18 and the control cock 3 being moved into the other pivoted position at an accelerated rate by means of the eccentric lever 18 arranged on the peg 42. In this way, the webs 8 and 8′ on the control cock 3 can be changed over more quickly than is possible through the movement of the slide 14 alone.

[0019]FIG. 4a shows a perspective partial view of the snap-action device, in which the eccentric lever 18 bears against one side of the recess 44 and holds the control cock 3 in the intended switching position. If the stop pin 17 comes to bear against that section of the eccentric lever 18 which projects from the control cock and pivots it a certain amount in the counterclockwise direction in FIG. 4a, the control cock 3 is, as a result, not moved out of its position as a result of the eccentric lever 18 being lifted off until the spring 20 starts to act as a result of the dead center position being exceeded and continues to rotate the peg 42 at an accelerated rate, so that the eccentric lever 18 comes to lie out of the position in FIG. 4a, on the other side of the recess 44, with the result that the control cock is switched over at an accelerated rate into the other switching position.

[0020] As shown in FIG. 3, in the exemplary embodiment illustrated, further grooves 6′, 6″ and 7′, 7″, which are in communication with corresponding cylinder bores 9′, 9″ and 10′, 10″ at which corresponding cylinder tubes 11 and 11′ are fitted, are formed next to one another on the circumference of the control cock 3. In a corresponding way, in each case three pistons 13 and 13′ are secured to the slide arms 14′ and 14″, and suction bores 4′ and 4″ and delivery bores 5′ and 5″ assigned to the respective circumferential grooves 6, 7 are formed in the valve block 2, as shown in FIG. 5. In this way, three adjacent individual pumps are formed at the pump unit 100, these pumps being driven and controlled in the same way.

[0021] The adjacent pumps and cylinder tubes may have different diameters, resulting in a three-stream pump which supplies three different delivery volumes. By way of example, the pump arranged on the smallest diameter of the cock and has the smallest piston/cylinder diameter may be designed for delivery quantities of from 1 to 1000 μl/h, while the middle pump, with a slightly larger piston/cylinder diameter, supplies 4 to 4000 μl/h. The pump provided on the largest diameter of the cock and having the largest piston/cylinder diameter may in this case, by way of example, deliver a quantity of from 10 to 10 000 μl/h.

[0022] The flows of substance delivered by the individual pumps are in a quantitative ratio which is dependent on the piston diameter. The three flows of substance can be combined with one another as desired by means of a downstream valve device (not shown). The flows of substance delivered by the three pumps may also be completely different media.

[0023] For the three pumps illustrated, the diameter of the cylinder tubes and pistons may also be designed to be identical. Depending on the intended use, the diameters of cylinder tube and piston can be matched to the particular requirements for the individual pumps.

[0024] The pump unit 100 having the three individual pumps can be adjusted continuously over the entire quantity range by means of control electronics (not shown) for the motor 201. The pump is self-priming and can produce high pressures.

[0025] The surface of the conical control cock 3 is lapped, so that it bears tightly against the correspondingly machined surface of the conical bore in the valve block 2, and consequently there is no need for separate sealing elements between the individual pumps or between the individual circumferential grooves.

[0026] The piston diameters are in each case designed to be greater than the width of the grooves 6 and 7 on the control cock 3, so that the piston 13 can come to bear against the surface of the control cock 3. As shown in FIG. 2, the front side of the pistons is of convex and beveled configuration so as to match the radius of the control cock in the region of the corresponding cylinder bore. The cylinder rod 30 is inserted into a central bore in the piston via an extension 31 of smaller diameter. An elastic element 32 is inserted between the end side of this extension 31 and piston 13, while the rear end side of the piston 13 has a slight play with respect to the section of the piston rod 30 of larger diameter. As a result, the piston 13 can be brought to bear against the circumferential surface of the control cock 3 in order to minimize dead spaces without an excessively high pressure being exerted on the circumferential surface of the control cock by the piston rod 30. The diameter of the cylinder bores 9 and 10 in the valve block 2 corresponds to the internal diameter of the cylinder tubes 11 and 11′, so that the cylinder bore in each case extends the cylinder space formed by the cylinder bore 9, 10.

[0027] The cylinder tube 11 is inserted into a receiving bore 22 in the valve block 2, with a sealing ring 34 being provided between the end side of the cylinder tube 11 and a shoulder between cylinder bore 9 and receiving bore 22. A clamping element 35 which surrounds the piston rod 30 and has an external screw thread is screwed into a threaded bore into the holding plate 12 in order to clamp the cylinder tube 11 in place (FIG. 3). This clamping element 35 bears against the outer end side of the cylinder tube 11 via a further sealing ring 36 and holds the cylinder tube clamped between the two sealing rings 34 and 36.

[0028] The outer end of the piston rod 30 is secured, via a retaining screw 37 in a bore in the slide arm 14′ or 14″, so that it is possible to effect precision adjustment of the piston position relative to the control cock 3.

[0029] To enable even extremely small delivery quantities to be delivered accurately with a piston stroke in the μ range, the force train between drive motor 201 and piston 13 of the pumps is designed to have no play. The motor 201 drives the intermediate gear 202 which is set to have no play and rotates the threaded spindle 203, which is mounted in bearings 209 and 209′, in the two directions of rotation without play when the direction of rotation of the motor is switched over. The nut 204 is of slotted design and is provided with a clamping element, for example a screw, which is indicated at 210, so that the engagement of the nut 204 with the threaded spindle 203 can be set without play.

[0030] On the motor 201 there is a flange 240 which has a recess in which an eccentric ring 241 with an external circumference is mounted. A further flange 242, which is secured to a stationary element 243 of the housing 220 via screws, is mounted on the inner circumference of the eccentric ring 241. Rotation of the eccentric ring 241 allows the toothing of the intermediate gear 202 to be set without any play, whereupon the two flanges 240 and 242 are fixedly connected to one another by screws 244.

[0031] The threaded spindle 203 is in engagement with a threaded ring 245 which is mounted rotatably in the bearing 209. On the opposite side, the threaded spindle bears against the bearing 209′ via a shoulder. The threaded spindle can be held clamped against the bearing 209′ by the threaded ring 245, so that the bearing of the threaded spindle is also free of play.

[0032] Finally, the bolt 205 protruding from the nut 204 is inserted, via a rigid spring element 211, into a bore 43 in the slide 14, so that it is also impossible for any play to occur at this connecting location. The spring element 211 between bolt 205 and bore circumference, may, for example, be a split washer which is wavy along its circumference.

[0033] The structure of the drive train between motor 201 and bolt 205 which is diagrammatically depicted in FIG. 6 is accommodated in the housing 220 of the drive unit 200, the bolt 205 projecting out of the front side of the housing 220 in a slot 213, as shown in FIG. 5. The control electronics (not shown) for controlling the motor 201, are also accommodated in the housing 220.

[0034] A spring-loaded bearing ball 216 (FIG. 5) is arranged on the front side of the housing 220 in a bore, this bearing ball, during assembly of drive unit and pump unit 100, coming to bear centrally against the rear side of the control cock 3 in order to hold the control cock in the axial direction with a predetermined bearing force in the conical bore of the valve block. The compressive force of the indicated spring 217, which acts on the bearing ball 216, can be altered by an adjustment device (not shown) in such a way that the bearing ball 216 bears against the planar rear side of the control cock with a predetermined compressive force. The frictional forces are minimized by the bearing ball bearing against the planar surface of the control cock.

[0035] To allow rapid release of the drive unit 200 from the pump unit 100, clamping elements 203 in the form of pivotable hooks are arranged on the opposite sides of the housing 220, interacting with pins 40 which protrude laterally from the base plate 1 of the pump unit 100. By way of example, four locating pins 231, which engage in corresponding locating bores 41 at the base plate 1 of the pump unit 100, are arranged on the front side of the housing 220. The hook-like clamping elements 230 may also be replaced by a single clamping bracket which connects the drive unit 200 to the pump unit 100.

[0036] This structure allows rapid release of the pump unit 100 from the drive unit 200, so that the pump unit can be sterilized, for example at elevated temperatures in an autoclave. In this case, the pump unit can be dismantled within a short time, with all the media-carrying components, such as pistons, cylinder tubes and control cock, being freely accessible for cleaning work. Correspondingly, the pump unit 100 can quickly be coupled to the drive unit 200 via the clamping elements 230, with the peg 205 engaging in the bore 43 of the slide 14 and the eccentric 43 engaging in the recess 44 on the rear side of the control cock 3. This engagement is guided by locating pins 231 which engage in the locating bores 41 in the base plate 1.

[0037] As a result of the pistons 13 bearing against the circumferential surface of the control cock 3, the metering pump is constructed in such a way that as far as possible no dead spaces are produced. If air should be sucked in by the suction bores 4 located at the bottom, this air will rise upward together with the delivery stream to the delivery bores 5, with any air bubbles which are present being moved to the delivery bores at an accelerated rate as a result of the pivoting movement of the control cock 3 during the switchover from the delivery stroke to the suction stroke.

[0038] In the exemplary embodiment described, the control cock 3 is switched over as soon as the pistons 13 have reached their limit travel, so that the drive direction of the slide 14 and the control cock 3 are reversed substantially simultaneously. By separating the changeover of the motor by the limit switches, on the one hand, and the changeover of the cock by the stop pins 17, on the other hand, it is also possible, by adjusting the limit switches 206 and 207, to change over the drive direction of the slide 14 without at the same time switching over the control cock 3.

[0039]FIG. 7 diagrammatically depicts another embodiment in a corresponding view to that shown in FIG. 1, with the valve block 2 having nonreturn valves 50 instead of a rotatable control cock 3. Two lines 4 a and 4 b, which lead to nonreturn valves 50 a and 50 b which open during the suction stroke of the pistons 13 and 13′, branch off from the suction bore 4. These nonreturn valves are connected to bores 51 and 52 which are formed transversely with respect to the cylinder bores 9 and 10 of the pistons 13 and 13′ in the valve block 2. The cylinder bores 9 and 10 of the opposite pistons 13 and 13′ open out into these bores 51 and 52 in the valve block 2. Further nonreturn valves 50 c and 50 d, which are connected to the common delivery bore 5 via lines 5 a and 5 b and open during the delivery stroke of the pistons 13 and 13′, are provided on the top side as seen in FIG. 7. During the suction stroke of the piston 13′ illustrated, the nonreturn valve 50 b lying on the suction side opens, while during the delivery stroke of the piston 13 the nonreturn valve 50 c which lies on the delivery side is opened. The bores 51 and 52 in the valve block 2, which lie substantially perpendicular to the cylinder bores 9 and 10, correspond to the grooves 6 and 7 of the control cock 3 shown in FIG. 1.

[0040] The diameter of these bores 51 and 52 is preferably designed to be slightly larger than the cylinder bores 9 and 10. As a result, the pistons 13 can move transversely into the bores 51, 52 during the delivery stroke and can come into contact with the bore wall, so that any air bubbles adhering to the pistons are released. The lines in the valve block 2 are designed in such a way that any air bubbles which may be present can rise upward and are guided out via the delivery bore 5. Accordingly, the lines in the valve block 2 are also designed in such a way that no dead spaces result.

[0041] The illustration in FIG. 7 provides only a diagrammatic illustration of the functional principle. Likewise, the volumes of the lines formed in the valve block 2 are designed to be small compared to the illustration shown in FIG. 7. For example, the length of the bores 51, 52 may even be only slightly greater than the diameter of the cylinder bores 9 and 10.

[0042] The arrangement of nonreturn valves 50 represented in FIG. 7 is present in the same way in the region of the other groups of pistons 13 lying opposite one another, so that in a plan view corresponding to FIG. 3 there are three successive groups of nonreturn valves 50 in the valve block 2.

[0043] In the diagrammatic illustration shown in FIG. 7, the valve block 2 is divided into a central block 2′, which has the bores 51 and 52 running transversely with respect to the cylinder bores 9 and 10, and two outer blocks 2″, in which the nonreturn valves 50 are formed. The valve block 2 may also be composed of a plurality of plate-like individual elements in order to facilitate production and line routing. The individual elements of the valve block 2 are connected to one another by diagrammatically indicated screws 54, so that the pump can easily be dismantled. It is preferable for metal plates 53, which are clamped together by the screws 54, to be provided on the top side and underside of the valve block 2; the screws 54 are guided through bores in the individual blocks 2′ and 2″ of the valve block and are anchored to the metal plates 53. As a result, the pump, after the screws 54 have been unscrewed, can very easily be broken down into its individual parts and then cleaned or sterilized. On the other hand, with this structure, in which the individual plate-like elements of the valve block 2 are held clamped as a stack between two outer metal plates, it is possible to generate pressures of up to 200 bar in the pump without leaks occurring.

[0044] Those elements of the pump which come into contact with the medium to be delivered, in particular the individual elements 2′, 2″ of the valve block 2 and the pistons 13 with cylinder tubes 11, are preferably made from Teflon or ceramic, depending on the type of media to be delivered.

[0045] In the embodiment shown in FIG. 7, the switching device 42, 43 represented in FIGS. 3 and 4 is absent as well as the control cock 3, since the switching between suction bore 4 and delivery bore 5 is effected automatically by the nonreturn valves 50. Otherwise, the structure of the metering pump shown in FIG. 7 corresponds to that shown in the previous figures in terms of the driving of the pistons and their arrangement and configuration or design.

[0046] In the structure shown in FIG. 7, the pistons can be individually adjusted more easily than in the embodiment shown in FIGS. 1 and 3, in which the position of the control cock 3 has to be taken into account when adjusting the pistons. This factor is eliminated by the automatically switching nonreturn valves 50. In the embodiment shown in FIG. 7, on account of the automatically switching nonreturn valves 50, it is also possible for the pump to be switched more quickly between the suction stroke and delivery stroke compared to the design with a rotatable control cock 3.

[0047] The nonreturn valves 50 in the valve block 2 also result in the metering pump operating without any pulsation, with the result that precise metering of the delivery medium is possible in particular at very small delivery quantities.

[0048] The pump itself can easily be separated from the drive unit 200, as shown in FIG. 5; the view shown in FIG. 5 substantially also corresponds to an embodiment which has the structure shown in FIG. 7 in the valve block 2.

[0049] The structure of the valve block 2 shown in FIG. 7 also simplifies the connection of the block-like drive unit 200 to the base plate 1 of the pump unit 100 (FIG. 5), since the coupling shown in FIG. 3 between eccentric lever 18 and the snap-action device accommodated in the drive unit is eliminated. The bearing ball 216 shown in FIG. 5 for adjusting the bearing pressure of the control cock is also eliminated. To separate the drive unit 200 from the pump unit 100, it is merely necessary for the clamping hooks 230 to be released, while during assembly it is merely necessary for the bolt 205 to be inserted into the bore 43 in the slide 14, with the locating pins 231 engaging in the locating bores 41 in the base plate 1 of the pump unit 100. Drive unit 200 and pump unit 100 therefore form structural units which are separated from one another and can be fitted together.

[0050] Various modifications to the design described are possible. For example, instead of the three individual pumps described, it is also possible to provide just a single pump having two cylinder tubes and two opposite pistons. It is also possible for the cylinder tubes 11 of a plurality of individual pumps to be combined to form a cylinder block, which is held so as to bear against the valve block 2 in the manner which has been described. 

1. A metering pump having pistons (13, 13′) which lie opposite one another, are guided in cylinders (11, 11′) and are connected to one another by a slide (14) which is moved in a reciprocating manner by a drive motor (201), a switching device (3) being arranged between the pistons (13, 13′) in a valve block (2), which switching device alternately connects the opposite cylinder spaces to a suction opening (4) and a delivery opening (5).
 2. The metering pump as claimed in claim 1, in which the switching device is designed as a control cock (3) which can rotate in the valve block (2) and is provided on the circumference with grooves (6, 7) which are separated from one another by webs (8, 8′) at diametrically opposite locations, one groove (6) being in communication with a cylinder bore (9) in the valve block (2) and the other groove (7) being in communication with a cylinder bore (10) formed on the opposite side in the valve block, and the one groove coming into communication with the suction opening (4) formed in the valve block as a result of the reciprocating pivoting of the control cock (3) while the other groove is connected to the delivery opening (5) formed in the valve block, and vice versa.
 3. The metering pump as claimed in claim 2, in which the control cock (3) is of conical design and is inserted into a correspondingly conical bore in the valve block (2).
 4. The metering pump as claimed in claim 2, in which further grooves (6′, 7′; 6″, 7″), which are in communication with corresponding cylinder bores (9′, 9″, 10′, 10″) and suction and delivery openings in the valve block, are formed next to one another in the axial direction on the circumference of the control cock (3).
 5. The metering pump as claimed in claim 2, in which stops (17, 17′) which are spaced apart from one another are provided on the slide (14), which stops, in the region of the limit positions of the pistons, act on a lever (18) arranged on the control cock (3) in order to switch over the control cock.
 6. The metering pump as claimed in claim 5, in which a snap-action device (19, 20), which pivots the control cock (3) at an accelerated rate when a stop (17) bears against the lever (18), is formed on the lever (18).
 7. The metering pump as claimed in claim 1, in which the switching device is formed by nonreturn valves (50) in the valve block (2), these nonreturn valves being connected to the suction opening (4) and the delivery opening (5) via bores (51, 52) which are formed transversely with respect to cylinder bores (9, 10) in the valve block (2), the cylinder spaces of the opposite pistons (13, 13′) opening out into these bores (51, 52).
 8. The metering pump as claimed in claim 7, in which the diameter of the bores (51, 52) in the valve block (2) is designed to be slightly larger than the diameter of the cylinder bores (9, 10).
 9. The metering pump as claimed in claim 7, in which the valve block (2) is composed of elements (2′, 2″) in plate form which are clamped between two outer clamping plates (53).
 10. The metering pump as claimed in the preceding claims, in which the cylinders are formed by cylinder tubes (11, 11′) which at the end sides are held by a clamping element (35) so as to bear against the valve block (2).
 11. The metering pump as claimed in the preceding claims, in which a plurality of cylinder tubes (11, 11′) are arranged adjacent to one another on the valve block (2), and a corresponding number of pistons (13, 13′) are arranged next to one another on the slide (14).
 12. The metering pump as claimed in claim 11, in which the cylinder tubes and pistons of the individual pumps have different diameters.
 13. The metering pump as claimed in the preceding claims, in which the valve block (2) with cylinder tubes (11) and slide (14) is arranged on a base plate (1) in order to form a pump unit (100) which is releasably connected to a block-like drive unit (200).
 14. The metering pump as claimed in claim 13, in which locating pins (231), which engage in locating bores (41) at the base plate (1) of the pump unit (100), protrude from the block-like drive unit (200).
 15. The metering pump as claimed in claim 14, in which at least one clamping element (230), which interacts with a corresponding engagement element (40) on the base plate (1), is arranged on the drive unit (200).
 16. The metering pump as claimed in claim 13, in which a bolt (205), which protrudes from a nut (204) in engagement with a threaded spindle (203) and engages in a bore (43) in the slide (14) at the pump unit (100), is provided at the drive unit (200).
 17. The metering pump as claimed in claim 16, in which a drive unit (201) drives the threaded spindle (203) via an intermediate gear (202) which is set without play.
 18. The metering pump as claimed in claim 17, in which the direction of rotation of the drive motor (201) can be switched over by limit switches (206, 207) which are actuated by the longitudinal movement of the nut (204) on the threaded spindle (203). 